Tire pressure monitoring systems are increasingly being used in motor vehicles in order to improve safety. As a rule, they are direct-measuring systems equipped with pressure sensors on the wheels. This presents the disadvantage that additional pressure sensors must be built into such systems.
DE 101 52 590 A1 (see also U.S. Pat. No. 6,799,129, which is hereby incorporated by reference herein in its entirety) describes embodiments of a tire pressure monitoring system and method for vehicles equipped with anti-lock braking systems (“ABSs”), especially vehicles having more than two axles. The tire pressure monitoring system described in DE 101 52 590 A1 is equipped not only with wheel sensors on the wheels of at least one axle in order to sense variables that depend on wheel rotation, but also with an ABS control unit, which logically combines the variables with one another and evaluates them with regard to changes in the rolling radii of the wheels, taking into consideration how the variables change as a function of driving operation. The ABS unit generates a warning signal if the change of variables caused by low tire pressure exceeds a preselected limit. In addition to, or as an alternative to, wheel sensors of the ABS system, which sense variables that depend on wheel rotation, such as wheel rotation speed or distance traveled by the wheels, the absolute tire inflation pressure of the wheels of at least one axle is measured and a warning signal is generated if the measured tire inflation pressure drops below a preselected setpoint pressure. The wheel-rotation speeds or distances traveled by the individual wheels or the sums of the wheel rotation speeds or of the distances traveled by diagonally opposite wheels are compared with one another in the ABS control unit, which generates a warning signal if the difference of the mutually compared distances traveled or of the wheel rotation speeds or the difference of the mutually compared sums of the wheel rotation speeds or of the distances traveled exceeds a preselected threshold value.